The aircraft was maintained in accordance with existing regulations. The pilot was qualified for the flight. It is common practice for helicopter pilots to take on and drop off passengers with the rotor running after an appropriate briefing has been given, as set out in Air Navigation Orders (ANO) Series VII. The practice is widespread in the industry and is accepted by both companies and passengers even though it involves some risk. To further decrease the risk on this occasion, the pilot had given this group of passengers a second briefing. Shortly after the pilot's attention was attracted by a noise behind him, he felt the aircraft tilt. He acted by reflex to try to regain control of the aircraft and thus prevent it from tipping over. At all stages of training, instructors stress that the pilot must react quickly and effectively when the aircraft tilts in one direction or the other. In general, helicopters do not tolerate strong tilts. They result in a static or dynamic rollover, often with serious consequences. Slipping backwards could be perceived in the same way and cause the same reactions. When the last passenger to disembark passed in front of the aircraft, he was struck by the main rotor. Since nobody saw what happened, it is difficult to determine whether the passenger was hit solely because of the slope, the slip or the tilt, or whether he did not follow the safety precautions given by the pilot. It is just as likely that the accident was caused by a combination of these events.Analysis The aircraft was maintained in accordance with existing regulations. The pilot was qualified for the flight. It is common practice for helicopter pilots to take on and drop off passengers with the rotor running after an appropriate briefing has been given, as set out in Air Navigation Orders (ANO) Series VII. The practice is widespread in the industry and is accepted by both companies and passengers even though it involves some risk. To further decrease the risk on this occasion, the pilot had given this group of passengers a second briefing. Shortly after the pilot's attention was attracted by a noise behind him, he felt the aircraft tilt. He acted by reflex to try to regain control of the aircraft and thus prevent it from tipping over. At all stages of training, instructors stress that the pilot must react quickly and effectively when the aircraft tilts in one direction or the other. In general, helicopters do not tolerate strong tilts. They result in a static or dynamic rollover, often with serious consequences. Slipping backwards could be perceived in the same way and cause the same reactions. When the last passenger to disembark passed in front of the aircraft, he was struck by the main rotor. Since nobody saw what happened, it is difficult to determine whether the passenger was hit solely because of the slope, the slip or the tilt, or whether he did not follow the safety precautions given by the pilot. It is just as likely that the accident was caused by a combination of these events. The pilot was qualified on the aircraft. All the passengers received a safety briefing. The landing ground sloped up at a grade of 8.5 degrees. The flight manual for the aircraft specifies that the maximum slope for landing and stopping the aircraft is 10 degrees in a nose-up attitude. Other passengers were disembarked at the same place earlier. On the ground, the pilot felt the aircraft tilt back and immediately regained control of it. The last passenger to exit the aircraft was hit on the head by the main rotor. Disembarking passengers while the aircraft is running is a common practice accepted by the industry and the authorities, but involves some risk.Findings The pilot was qualified on the aircraft. All the passengers received a safety briefing. The landing ground sloped up at a grade of 8.5 degrees. The flight manual for the aircraft specifies that the maximum slope for landing and stopping the aircraft is 10 degrees in a nose-up attitude. Other passengers were disembarked at the same place earlier. On the ground, the pilot felt the aircraft tilt back and immediately regained control of it. The last passenger to exit the aircraft was hit on the head by the main rotor. Disembarking passengers while the aircraft is running is a common practice accepted by the industry and the authorities, but involves some risk. One of the passengers was hit by the main rotor while passing in front of the aircraft; it was impossible, however, to determine the exact moment and circumstances of the occurrence.Causes and Contributing Factors One of the passengers was hit by the main rotor while passing in front of the aircraft; it was impossible, however, to determine the exact moment and circumstances of the occurrence.